The invention generally is directed to mill trains with at least one roll stand for rolling rolling stock, whereby the roll stand is driven by at least one A.C. motor (AC motor). More particularly, the invention is directed to mill trains having a great range of speed adjustment such as disclosed in U.S. Pat. No. 4,882,923, which is fully incorporated herein by reference.
The mill train disclosed in U.S. Pat. No. 4,882,923 comprises electric motors for driving at least one of the roll stands whose ratio of maximum to minimum rolling speed amounts to at least 3.0, but at most 10.0. It is expected of the drive motor that is disclosed in U.S. Pat. No. 4,882,923, and that is not regulated in any special way, that it exhibits an unchanging power output according to its continuous rated output in the described speed range. Given a A.C. motor, however, a range of control with constant power output can only be realized with an additional outlay of components that is all the greater the greater the range of control.